Fault Current Limiter(FCL)
Nowadays, the power generation capacity is increasing continuously to support more and more industry consumptions around the world.
The increasing generation in high load density networks or interconnections between systems, had significantly increased the short-circuit power on the power grids. If the short-circuit current rating of the equipment in the system had been exceeded, the switchgears would not be capable to switch off the fault currents safely under system fault events. Then those equipments must be either upgraded or replaced, both of which are under high cost and time-consuming.
Luckily, FACTS technology offered a solution called fault current limitation with clear benefits in such cases. FCL, short for “Fault Current Limiter”, is a new technology composed of an electronic controlled series capacitor and a series reactor. This new device operates with zero impedance in normal operation conditions (capacitor + reactor, identical impedance but counteracting with each other); and when in case of an unexpected short circuit fault, it will switch to an obvious inductive impedance within a few milliseconds by bypassing the series capacitors while leaving only the series reactors on line. See Fig 3 for illustration. As a result, the newly appeared inductive impedance will significantly increase the line impedance and then successfully decrease this line short-circuit current to an acceptable level. That’s why it is called “Fault Current Limiter”.
The FCL (Fault Current Limiter) connects in series in the power transmission lines.
There are two types of FCL, one is FSC-type FCL, which is shown is figure 1. Normally, the LC is connected in series in the circuit, working in a resonance state, and the impedance is 0ohm or very small. When the controller detects a fault state, it quickly triggers the spark gap and bypasses the capacitor banks, the line impedance increases sharply at the same time, thus the fault current is quickly suppressed. Its impedance characteristic is shown in Figure 3.
Figure 1. FSC type FCL
The other is TPSC-type FCL, which is shown in Figure 2. Normally, the thyristor series valve is blocked, and the LC is connected in series in the circuit, working in a resonance state, and the impedance is 0 or very small. When the controller detects a fault state, it quickly turns on the thyristor series valve, the line impedance increases sharply at the same time, and the fault current is quickly suppressed. Its impedance characteristic is shown in Figure 3.
Figure 2. TPSC type FCL
Figure 3. Impedance characteristic of FCL
RXPE FCL installation is placed as following typical layout (Fig 4).
Figure 4. 3D Drawing of FCL(Schematic)
With FCL, the system impedance will increase significantly after the short circuit occurs, and the short circuit current will be suppressed to the safety value immediately. The performance of FCL is shown in figure 5.
Figure 5. Comparison of short circuit current with and without FCL
The following figure shows the time sequence of FCL equipment operation:
Figure 6. Time sequence of FCL equipment operation
RXPE FCL is a good and reliable measure to reduce high fault currents to acceptable level where the max short-circuit currents had exceeded the ratings of existing switchgears.
More information please contact RXPE 7*24h service hotline +86-1834 12 12 126.
